1. Field of the Invention
The present invention relates to an image forming apparatus that detects occurrence of a jam, and more particularly to an image forming apparatus having a conveyance roller for conveying paper.
2. Description of the Related Art
Electrophotographic image forming apparatuses include MFPs (Multi-Functional Peripherals) having scanner, facsimile, copy, printer, data communication, and server functions, facsimile machines, copiers, and printers.
In an image forming apparatus, when a jam (paper jam) occurs, the user of the image forming apparatus opens the door of the casing of the image forming apparatus and removes paper that causes the jam in order to clear the jam. In general, paper that causes a jam (hereinafter also called jammed paper) is sandwiched between rollers for conveying paper in the inside of the image forming apparatus. The user pulls out the jammed paper from between the rollers thereby clearing the jam. This process is called jam handling.
In jam handling, the force exerted by the user to pull out jammed paper rotates the roller, whereby a motor coupled to the roller is rotated. The rotation of the motor produces regenerative power (regenerative energy by self-power generation of the motor). Back electromotive force (back electromotive voltage) of this regenerative power may break down a load (device) in the image forming apparatus that is connected to the same power system as the motor.
Document 1 below discloses a technique for protecting a load from back electromotive force. According to this technique, if external force rotates a motor, a motor control device decelerates the rotation of the motor thereby preventing overvoltage due to induced voltage.
Document 1: Japanese Laid-Open Patent Publication No. 2011-103707
In order to prevent accidental rotation of the motor and to ensure the user's safety, power supply from the power source to the motor is preferably cut off. In the technique in Document 1, however, it is impossible to cut off power supply from the power source to the motor because it is necessary to supply power to the motor in order to decelerate the rotation of the motor.